1. Field of the Invention
The invention relates to the lighting arts. It is especially applicable to the packaging of light emitting diodes (LED's) to form a spot light, flashlight, or other lamp type that produces a collimated or partially collimated beam, and will be described with particular reference thereto. However, the invention will also find application in packaging of LED's, semiconductor lasers, halogen bulbs, and other light emitting elements for spot lighting, flood lighting, and other optical applications.
2. Discussion of the Art
Spot light lamps emit a collimated or partially collimated beam of light (e.g., a conical beam), and are employed in room lighting, hand-held flashlights, theater spot lighting, and other applications. Examples of such lamps include the MR-series halogen spotlights which incorporate an essentially non-directional halogen light bulb arranged within a directional reflector, such as a parabolic reflector. The MR-series halogen spotlights are commercially available with or without a front lens, and typically include electrical connectors disposed behind the parabolic reflector, i.e., outside of the range of the directed beam. The reflector, optionally in cooperation with a front lens, effectuates collimation of the halogen light bulb output to produce the collimated or conical light beam. The MR-series spotlights are available in a range of sizes, wattages, color temperatures, and beam angles. However, the MR-series spot ights do not include adjustable beams.
The Maglite® flashlight is a prior art device that has an adjustable spot beam. An incandescent light bulb is arranged inside an essentially parabolic reflector. This device effectuates a variable beam angle ranging from a narrow spot beam to a wide, “flood” beam, by including a rotating actuator for moving the reflector axially with respect to the incandescent bulb. This arrangement suffers from significant beam non-uniformity when the light source is strongly defocused. Under conditions of extreme defocusing, the Maglite® flashlight beam exhibits a black spot at the beam's center.
Lamps which utilize one or more LED's as the source of light are becoming more attractive as the light output intensities of commercial LED's steadily increase over time due to design, materials, and manufacturing improvements. Advantageously for spot module applications, commercial LED's typically have a lensing effect produced by the epoxy encapsulant that is usually employed to seal the LED chip from the environment. Hence, these commercial LED's are already somewhat directional, and this directionality can be enhanced using an external lens. Additionally, LED's that emit white light of reasonably high spectral quality are now available. In spite of continuing improvements in LED light output, at present an individual LED is typically insufficiently bright for most lighting applications. Nonetheless, due to the small size of LED's, this intensity limitation can be obviated through the use of a plurality of closely packed LED's that cooperate to produce sufficient light.
Application of LED's to spotlighting applications, and especially to spotlighting applications in which the LED-based lamp is contemplated as a retrofit for replacing an existing lamp that employs another lighting technology (e.g., a retrofit for replacing an MR-series halogen lamp) is complicated by the use of multiple LED's as the light source. The spatially distributed nature of an LED source array greatly reduces the effectiveness of conventional parabolic reflectors which are designed to collimate and direct light emanating from a point source, such as light generated by a halogen or incandescent bulb filament. Furthermore, a front lens of the type optionally included in an MR-series halogen spot lamp is ill-suited for collimating light from a plurality of LED's, because most of the LED's are not positioned on the optical axis of the lens. Thus, the optical systems of existing spot lamps, both with and without variable beam angle, are relatively ineffective when used in conjunction with LED light sources.
The present invention contemplates an improved light source or lamp that overcomes the above-mentioned limitations and others.